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The value of salt marsh as a sea defence

                                            Marine Pollution Bulletin, Vol. 30, No. 3, pp. 180-189, 1995
                                                      Copyright © 1995 Elsevier Science Ltd
                        0025-326X(94)00173-1
~    Pergamon                                            Printed in Great Britain. All rights reserved
                                                           0025-326X/95 $9.50+0.00




The Value of Salt Marsh as a Sea
Defence
SUSANNA E. KING* and JOHN N. LESTERt
*Imperial College Centrefor Environmental Technology, and
t Environmental and WaterResource Engineering Section, Department of Civil Engineering,
Imperial College of Science, Technologyand Medicine, Imperial College Road, London SW7 2BU, UK



                                 1992a). A further 900 m is protected solely by wide
The value of salt marsh as a buffer outside sea walls is
                                 swathes of salt marsh, which can be defined as areas
appraised. As salt marsh width decreases an almost
                                 vegetated by herbs, grasses or low shrubs, bordering
linear increase in wall height is necessitated until loss
                                 saline water bodies (Adam, 1990). Where a wide
of a final thin strip causes an exponential rise in main-
                                 expanse of vegetated ground lies seaward of protected
tenance and construction requirements and costs. A
                                 land, a simple clay bank may offer sufficient protection
minimum value is placed on salt marsh in its capacity
                                 from flooding. It has been widely acknowledged that a
as a sea defence and its use and non-use values are dis-
                                 generous width of salt marsh, with optimal protection
cussed. Except in special circumstances salt marsh has
                                 value at 50-80 m depending on site (Hydraulics
a low capital value, and while sale of land to wildfowling
                                 Research, 1987), can dramatically reduce the con-
syndicates is found to be the highest direct value, this is
                                 struction costs of sea defences. The Anglian Region of
far surpassed by the indirect value of savings on both
                                 the NRA uses a sliding scale of wall construction costs
capital and maintenance costs in sea defence terms.
                                 and requirements which is linked to the degree of
Reference is made to the coast of East Anglia in the UK
                                 protection from salt marsh. Many Essex salt marshes
and in particular to that of Essex.
                                 are at present in decline (Brampton, 1992), which is
                                 putting increasing pressure on flood defences and has
                                 economic as well as environmental implications. An
The responsibility for the protection of the Essex coast     average rate of horizontal erosion at the interface
and tidal estuaries (Fig. 1) lies with the National Rivers    between mud flat or creek edge and vegetated marsh on
Authority (NRA) which maintains 440 km of sea           an estuarine bank in the environs of the River
defences against flooding of low-lying land (NRA,         Blackwater in Essex, for example, has been measured




                                      I ]3~eov     ~   Water
                                    j/  ....  ":_~Blackwater

                                       "x~_ ~    River Crouch
                                        ~     Thames estuary

                       Fig. 1 M a p showing site locations.


180
Volume 30/Number 3/March 1995


as 2 m yr -~ over a 2 year study by the Institute of    and reduction of flood damage but their sea wall
Estuarine and Coastal Studies (IECS), while an open     protection function was not noted and was therefore
coast marsh lost an average of 4.01 m yr -1 and a      absent from the economic analysis. It is very difficult to
sheltered creek bank an average of 0.305 m yr -1 (IECS,   price the functions of shelter and of landscape value for
1993). These losses are attributed to wave action and a   recreational use, the intrinsic value of salt marsh as a
long-term change which is thought to be due to the     landscape form and its value to conservation and
increase in wave energy at the shore, which in turn is   scientific research at ecosystem, habitat and species
attributed to increasing nearshore depths caused by a    level. Until the last decade, salt marsh has often been
local rise in sea level relative to the coast. In East   conceived as coastal wasteland with minimal economic
Anglia the average rise is 2 mm yr -1 but it increases to  value, which has led to considerable loss through land
approximately 4 mm yr -1 for the area south of the River  reclamation for use as agriculture, caravan sites,
Blackwater (NRA, 1991a). Such local anomalies are      industrial developments and marinas. In the following
explained by a combination of eustatic changes in      pages comparative values towards the valuation of salt
regional sea level and long term tectonic land move-    marsh for direct and indirect use are suggested in order
ment in the southern North Sea. Ministry of Agri-      to stimulate the debate on economic appraisal of these
culture, Fisheries and Food (MAFF) guidance to sea     fragile systems and in the hope that such considerations
defence authorities advises an allowance of 6 mm yr-~    will be taken into account in the development of
for relative sea level rise in Anglian, Thames and     management strategies encompassing complete valu-
Southern regions. 'Sea defence' applies to measures     ation of salt marsh.
taken against flood hazard as compared with 'coastal
defence' which encompasses all aspects of defence      Salt marsh and the concept of "total economic value'
against coastal hazards (floods or erosion), thus       Any attempt to place a value on salt marsh as a
including 'coast protection' which refers to measures    discrete economic unit will be a complex process. While
taken against erosion of the land and other encroach-    it is feasible to give the economic value in terms of
ments by the sea (MAFF, 1993a).               simple values tied to sea walls, many questions need to
  Even without a scenario of global sea level rise,    be answered if indirect values and qualities with no
                              monetary value are to be incorporated. Salt marsh
which present best estimates are reducing in severity
(Intergovernmental Panel on Climate Change, un-       products are a tangible output and can be considered as
                              direct use values while those associated with salt marsh
dated), local conditions mean that the outlook for the
Essex salt marsh is not encouraging as sea defences     functions or contributions to the wider environment
prevent their landward shift and limit their ability to   have to be indirectly inferred (Winpenny, 1991) and
react to rapid ecological disturbance. A rise in relative  would become indirect use values. When summed such
                              factors would yield a minimum value which would
sea level is likely to increase the tidal prism of an
estuary, lengthening the shore profile which will result  exclude many unquantified facets, each of which would
in a squeeze of salt marsh balanced by a gain in mudflat  add positive value to the salt marsh in question. By
                              combining values calculated from the products and
area. Mudflats seaward of the vegetated zone are
                              functions of an ecosystem with those derived from the
integrally involved in the local sediment transport
                              less easily evaluated fields of options for future use, plus
regime and sediment movement between these
                              non-use existence values, steps can be taken towards
morphological units is likely to be cyclic (Pethick,
                              achieving a 'total economic value' (Pearce, 1993).
1992). This will lead to wider, shallower cross-estuarine
                              Option values are related to use values in that a value is
profiles and a loss not only of high salt marsh but also
                              placed on the retention of, for example, a wetland for
of mid-marsh vegetation communities. In the light of
                              possible future use or, termed bequest value, for use by
predicted sea level rise, Boorman (1992) has predicted
                              future generations (Barbier, 1993). Existence value is
a replacement of present salt marsh vegetation by that
                              concerned with the preservation of a system or species,
from a lower zone in any affected area. In addition to
                              in this case salt marsh, in its own right and is not related
sea defence implications, this will have a detrimental
                              to present or future use, the latter case being a non-use
effect on the habitat value of terrestrial invertebrates
and birds, found most frequently in high salt marsh and   form of bequest value.
bordering environments (IECS, 1993).              Of the direct use values which can be identified in
                              connection with salt marsh, wildfowling stands alone in
  The loss of salt marsh along the east coast is causing
                              that a substantial sum can be commanded for shooting
concern in terms of sea defence and conservation but
the economic reality has yet to be fully addressed. As   rights, either by sale or by lease. Although wildfowl are
yet few attempts have been made to value salt marsh in   a product of the marsh, the value to wildfowlers is in the
                              sport as opposed to the price of the individual birds
monetary terms. In North America, Gosselink et al.
                              that they shoot. Rent and sales to wildfowlers should be
(1974) evaluated tidal marshes in the context of
                              taken into consideration in valuation but the difference
extensive loss to development and degradation by
                              between perceived value and actual prices paid can be
overloading of waterborne waste. An assumption was
                              difficult to reconcile. Indirect values can be assigned to
made that the full value of coastal fisheries and
                              salt marsh by relating area to the reduced cost of
products of aquaculture could be related to tidal
                              defences in places where a salt marsh buffer is present
marshes; their waste assimilation role was quantified
                              on the seaward side of a sea wall and this can be com-
and primary productivity estimates were used. Little
                              pared with agricultural land values directly landward
mention was made of their role in energy absorption

                                                          181
                                                          Marine Pollution Bulletin


of the sea wall or in the area protected by the wall.
Property prices in vulnerable places can also enter the
equation in individual cases. Salt marsh has an                        TOTALECONOMICVALUE ,1
ecologically and economically important role as a
transitory habitat for fish, providing sheltered feeding
and nursery grounds; in addition a flux of nutrients into

                                 IUSE!ALUESI
the tidal waters (Long & Mason, 1983) becomes an
                                                              I NON-USEVALUES
integral part of the rich estuarine ecosystem, products
                                  I
of which include fish, oysters and worms for angling
bait. Ecological research into salt marsh as a functional
                                I
unit has resulted in attempts to quantify productivity
                                DIRECTUSE
and nutrient flows (Lefeuvre et al., 1993), offering a      VALUES
potential understanding of their value in nutrient supply    wilclfowling              oplion of      poterttialuse for
                                        sea delonea
                                 grazing    oyster pmdu~on     future       descendants
and exchange.                          Salicomia   coastal fishedes    personal use
                                        b~t ~ n g
                                 harvest
  Unquantifiable environmental factors, such as values             MOOovershoot
to conservation and recreation, have traditionally been             recreation - shelter
                                               scenery
undervalued and left out of the benefit-cost equation.                    birdlife
                                        scientific,
However, alongside an increased awareness of environ-              conservation
                                        and educational use
mental systems, a number of methods by which the
                                                                  I         I
intangible facets of the environment can be estimated
and incorporated into a scheme of monetary value have                          retention of salt        not related
                                                    marsh for future        to use
been developed. In a review undertaken for the NRA of                          generations
the various approaches to total valuation of the natural
environment appropriate to the case of sea defence,      Fig. 2 Use and non-use values of salt marsh. Source: adapted from
                                   Barbier (1989).
Penning-Rowsell et al. (1992) selected the contingent
valuation method (CVM) as the most appropriate
means of valuing coastal sites. No detailed analysis is
yet available for salt marsh but this is the only method   engineering costs or, more significantly, on research into
which may be used to investigate the magnitude of       methods of containing the current situation and on
direct use, indirect use and non-use values when       undertaking urgently needed large scale experimental
seeking to determine the total economic value of the     projects to encompass modern geomorphological
resource.                           theory.
  Values are assigned to each product and function of
the salt marsh. Those which are not easily valued are     Value from land prices and income
costed on a 'willingness to pay' scale of prices, reached     Wildfowling. Income from salt marshes in Essex is
by thorough testing using questionnaires devised to      very small apart from sales to wildfowlers and licenses
avoid, where possible, the associated hazards of       for shooting rights.* A north Essex farmer was recently
inaccurate resposes. Penning-Rowsell et al. (1992)      offered £70 000 for annual shooting rights to 142 ha
includes examples of such methods in practice. Figure 2    (350 acres) of grazing marsh (unimproved reclaimed
indicates the difficulty which arises when some indirect   salt marsh) and salt marsh. At £493 ha -l yr-1 (£200
use values can be discussed according to a monetary      acre -~) to provide high level syndicate shooting of
system while others become aligned with the intangible    pheasant, partridge and duck this price reflects the
non-use values. Within these last two categories are     difficulty inherent in placing a value on such land,
option value (willingness to pay for use of environment    especially in the many instances where saltings outside
in the future) and bequest x;alues, which have both use    the sea wall are included in the price for shooting on
and non-use values (willingness to pay for benefit of     grazing marsh within the sea wall. In 1989, 73 ha (180
ones descendants' future use of the salt marsh plus a     acres) in north Essex were sold to local wildfowlers for
wish to retain options for descendants to live in a time   £80 000 (£1096 ha -1, £444 acre-1) although the land
when salt marsh still exists in that particular place). The  valuation at the time was £54 000. In the same area in
latter is unassociated with actual use and puts some     1992, 60 ha (150 acres) were sold for £22 500 (£370
                               ha -l, £150 acre-l). This difference not only reflects a fall
store on wilderness in built up areas. Existence value is
similarly not associated with actual use but with the     in land prices but also competition between potential
existence of species or ecosystems.              users of salt marsh, as in the former case the wild-
  A summation of direct values, such as profit from     fowlers were concerned that a conservation organiza-
land rent or sale and any other form of local financial    tion would purchase the land and ban all shooting.
gain, plus any other quantifiable indirect value, plus    Competition between wealthy wildfowling syndicates
other use and non-use values can be made to give a      can also inflate prices. An example is the Norfolk
minimum value to salt marsh, which any other         grazing marsh which was recently sold for £9884
identified but as yet unquantified values would increase.   ha -1 (£4000 acre-l). When such artificial escalation
This value could then be counted in benefit-cost       of prices occurs, conservation interests are usually
equations to work out how much should be spent on
either protecting salt marsh in its capacity as a buffer to   *Sources on land sales are confidential but can be verified.


182
Volume30/Number 3/March 1995

outpriced. There is frequently little correlation between   at their disposal and who regard wildfowling as a
the price of land rental and the value of shooting       smarter form of pheasant shooting, since wildfowl are
activities, taking account of factors such as available    not artificially produced for the sport.
birds, varying weather conditions and the time available     In addition to (and frequently alongside) wildfowling
to the membership for shooting. A schism can be        interests, land can be part of a working farm which
identified between local wildfowl clubs, frequently with    might include use for grazing. In Essex salt marsh and
a small membership and limited funding and large        sea wall grazing is of use only as part of individual
consortiums of non-local people who are prepared to      management systems which are offset by subsidies.
pay considerably more than could be expected for high     Grazing by sheep is considered advantageous to sea
quality shooting rights.                    wall structure (by compaction without too great a
  The Crown Estates Commissioners (CEC), who         weight and by keeping the sward short and compact,
have historically sold inter-tidal land and currently own   thus making the wall less likely to fissure or to need
about 55% of the Essex foreshore, prefer to price salt     mowing). It also aids the ecological diversity of the
marsh rental for any purposes on the approximate        vegetation and associated invertebrates. In the Ribble
linear length of foreshore at the high water mark. This    estuary on England's west coast (see Fig. 1), annual net
costs £120-£150 per km depending on various factors.      income from grazing in a salt marsh nature reserve has
A shooting lease will generally cover the ground        been valued at £17 000 for 1113 ha (2750 acres) which
between mean high water (MHW) and mean low water        can be regarded as £15.27 ha -I yr-1 (£6.20 acre -j yr-I).
(MLW) but valuation is based on a CEC premise that       This difference in ability to generate income is likely to
most of the relevant activities take place around high     rest on the morphological dissimilarities between
water where there is most cover for wildfowl, whereas a    marshes on the coastal areas under discussion. In
wide open stretch of vegetated salting may be fairly      France premium prices are paid for salt marsh-grazed
unattractive to these birds, hence the emphasis on a      lamb. This distinction does not appear to be made in
linear policy. The Commissioners, in company with       the United Kingdom although it is acknowledged that
other lessors of salt marsh, alter the scale of charges    salt marsh provides clean, parasite-free ground which is
                                a bonus for stock health.
depending on activities or use. A low rent is likely if
                                 In most areas of the United Kingdom with extensive
conservation interests are uppermost while shooting
                                salt marsh, glasswort (Salicornia spp.) is harvested for
rights are likely to attract a higher return. This is itself
                                personal consumption and in parts of East Anglia it is
qualified by other factors, such as the management and
                                harvested as a crop for sale locally and in London
policing of an area by the incumbent wildfowlers; in
                                markets as a luxury item. Records are not kept of sales
some cases such services outweigh any financial
                                figures which are likely to be insignificant on a
advantage and rents are purely nominal, and charged
                                production/acreage scale but make some contribution
merely for reasons of legality. A Hamford Water
                                to the local economy.
explosives factory has a reciprocal agreement with a
wildfowling club which enjoys free shooting rights in
                                Valuesfrom use of the environment
exchange for their presence on the salt marsh. This is a
                                 Sea defence value. The data in Table 1 may be used to
useful addition to security arrangements and provides
                                calculate a value (£ m -e) of salt marsh based upon the
indirect value in the difference between security costs
                                saving which is made as a consequence of the
without wildfowlers present.
                                protection afforded to the sea wall and includes
  Positive management by wildfowlers can include the
                                calculation of a similar saving by reference to linear sea
building and maintaining of bridges over creeks (thus
                                wall. Wide expanses of vegetated marsh are valued, in
allowing access to otherwise inaccessible distant areas,
                                this way, at a lower price per unit area than thin strips
in some cases a questionable advantage); production of
                                which run along the toe of the sea wall. This artificial
a wildfowling plan to be approved by all interested
                                valuation makes no concession to the fact that in many
bodies such as English Nature, the Royal Society for the
                                situations a thin strip is less likely to be sustainable than
Protection of Birds (RSPB) and the CEC; the setting
                                a larger area but is useful to illustrate the cost of salt
aside of refuge areas and nesting sites; record keeping
                                marsh loss in these circumstances.
and bird counts throughout the winter. In sensitive
                                 Figure 3 indicates that the first 6 m width of salt
areas where access by the general public is not advanta-
                                marsh beside the sea wall would appear to save between
geous to management or security, the occasional
                                £1500 and £3500 m -1 length of wall comparing the cost
presence of wildfowlers is claimed to act as a deterrent
                                of building a 12 m wall with that of building a 6 m wall
not only against unlicensed individuals but also against
                                protected by a 6 m strip of salt marsh. This depends on
unwanted recreational use. This last point is tempered,
                                the type of wall construction used which, in turn,
however, by the fact that wildfowling takes place mainly
at dawn and dusk in the winter months whilst much       depends on various environmental and economic
                                factors and would give salt marsh immediately adjacent
recreational use takes place in the summer. A further
                                to a sea wall a value of between £250 and £600 m -2. At
facet to this equation are the land owners whose
                                the given intervals, the next 24 m of salt marsh saves
shooting rights have traditionally been set by barter
                                £700 m -1 length of wall (£30 m -2 of salt marsh),
with locals; the two-way flow of goodwill in small
                                comparing the cost of building a 6 m wall with that of
communities is not quantifiable in monetary terms.
                                building a 5 m wall. The next 30 m saves £10 m -2 of salt
There is a parochial distrust of relatively new organized
                                marsh and the outer 20 m £5 m -2 of salt marsh.
groups of non-local wildfowlers which have large funds

                                                            183
                                                                              Marine Pollution Bulletin


                                              TABLE 1
              Comparison of sea wall building and maintenance costs and savings with amount of salt marsh protection.

                                                               Saving on building        Saving on cost of
                  Wall height      Cost of new wall          Maintenance cost        cost of new wall         wall maintenance
Width of salting
                   (m)*          (£ m-')*             (£ m -1 yr-I) *         (£ m -1 wall)t          (£ m -1 wall)t
(m)*
                      3            400                 1              2600-4600                49
80
                      4            500                 5              2500-4500                45
60
                      5            800                15              2200-4200                35
30
                      6           1500               25-30             1500-3500               20-25
6
                     12          3000-5000               50                0                   0
0

   *Source: NRA (1992b).
   tCalculated data.


                                                 more still remains and this increase in savings with
Wall height (m)                  Saltmarsh width (m)
                                                 width of salt marsh reflects most accurately the value of
12 10 8 6          4    2   0 10 20 30 40 50 60 70 80
                                                 wider swathes of salt marsh in sea defence. This would
                      [                           give a blanket value of 60p m - : to those wide expanses,
   12m wall
                                                 which at nearly £6000 ha -~ (£2400 acre -1) is in excess
                                                 of the value of most Grade 1 agricultural land. If
                                                 regarded in strips as progressive loss occurs, the outer-
                                                 most salt marsh would save 20p m -a and the final 6 m
                                                 would save between £3 and £4 m -2. At the last com-
                                                 prehensive survey in 1983, 300 km of Essex sea walls
                                                 had a salt marsh toe, this reduces to about 220 km
                                                 where more than a narrow strip is present. However, at
                                                 present sea walls are still being constructed using the
                                                 scale illustrated in Table 1 but ignoring the fact that in
                                                 places there is an arguably non-sustainable (in the short
                                                 term) width of salt marsh (NRA (M. Dixon), pers
                                                 comm., 1994a). Maintenance cost varies from year to
    LEGEND:
     Sallmassh    Value as protection   Saltmarsh beads
                             in        Protection value
                                                 year and ih Essex the average cost for tidal and sea wall
             outside sea wall(£ m2)               of strip (£ m 2)
     width (m)                 outside sea wall
                                                 maintenance is £2 188 000 yr -1, protecting 431 km at
                            61-80     I      5
      80    ~      30-60
                                                 an average £5.00 m -1 yr -1 (NRA, 1991b, 1992a,
                                   KN 1o            1993a). This corresponds with a hypothetical sea wall
                                                 height of 4 m and a salting width of 60 m.
                 7o.1,o         -3o     Ni     3o

                                                  Wall height (m)                  Saltmarsh width (m)
                                                  12 10 8 6          4   2   0 10 20 30 40 50 60 70 80
                                                  l''
   Fig. 3 Saving afforded by salt marsh on capital wall-building costs.
                                                   12m wall
                                                             ~l,~         i;;!                       ;
                                                                                ',    ,~    ;   ',
  Evaluation of an 80 m width of salt marsh as a whole
rather than in hypothetical strips permits a comparison
with the cost of sea wall rebuild in a situation with no
salt marsh. This yields a saving of at least £2600 m -x
length of wall (rising to £4600 at the top construction
rate) and a blanket value over the whole area of
between £30 and £60 m -2 or £300 0 0 0 - £ 6 0 0 000 ha -1
(£121 4 0 0 - £ 2 4 2 800 acre-l), which is approximately a
300-fold increase on the highest price a wildfowling
group might pay.
  In reality these figures will be obscured by the fact
that maintenance of banks is the norm in preference to
building new embankments or walls and that as salt
                                                    LEGEND:
marsh is lost, piecemeal measures are taken to improve                          Saitmarsh     Valueas plotection   Sallmwsh bands
                                                                              in           Protection
                                                                                              value
                                                     width (m)    outside sea wall (£ m2)  outside wall
                                                                              sea          of slrip (£ m2)
wall structures, resulting in a situation where each
                                                      80~          0.61         61-80    m          0.20
stretch of wall must be treated individually. Mainten-
ance figures, illustrated in Table 1 and Fig. 4, exhibit a                         60    ~--~     0.75         31-60    ~    I     0.33
similar but less costly gradation from an annual saving
                                                      30    ~       1.17         7-30     ~         0,42-0.63
of £ 2 0 - £ 2 5 m -1 length of wall (cutting the highest
maintenance costs by almost half) where only 6 m of                             6    1       3.3-,         6     1         3.30-,
marsh are left to protect the toe of the wall to a saving
of £49 m -1 wall length where a full width of 80 m or                        Fig. 4 Saving afforded by salt marsh to sea wall maintenance costs.


184
Volume 30/Number 3/March 1995


  If the Essex salt marsh continues to erode at the      between income forgone by farmers and the level of
current rate (an average of 19% of vegetated marsh was     payments, seen in the context of alternative aid in the
lost from the seaward side of Essex sea walls between     form of subsidies. The scheme is only practical where it
1973 and 1988 (after Burd, 1992) both capital and       is compatible with flood defence concerns.
maintenance spending on sea defence would seem          At least 20 areas of housing in Essex have salt marsh
bound to increase. A comparison with Norfolk and        protection outside sea walls; some are single farms or
Suffolk indicates that 426 km of tidal and sea defences    houses, others can be extensive, including whole
are maintained at an average of £2.70 m -1 yr-~ (NRA,     villages such as Salcott on the River Blackwater.
1991c, 1992c, 1993b). This difference can be explained     Techniques of valuation which analyse the relationship
by the extensive areas of sea coast in Norfolk and       between certain environmental quality characteristics
Suffolk which have sand dunes, salt marsh or a         and price of private goods are those of property value,
combination of the two as a first line of sea defence     land value and the hedonic price method (Hufschmidt
                                et al., 1983). The latter method, whereby the environ-
backed only by low clay banks with little need for hard
defences. A closer link can be made with the ronds of     mental variables which affect market value are dif-
the Norfolk Broads. These are linear stands of brackish    ferentiated and evaluated, would be likely to reflect a
or saline marsh which form buffer strips on the tidal     considerable devaluation where flood protection is
rivers between the sea wall and main fiver channel.      reduced by lack of salt marsh. The hedonic pricing
                                method could also be used where agricultural land is
Erosion caused by boat wash and a number of lesser
                                protected by salt marsh but a greater differential could
factors results in loss of the rond with consequent need
                                be expected to occur in the case of property, where
for expensive and unsightly sheet steel piling. By the
                                prices are higher and the perceived consequences of
same comparison one could tentatively value vegetated
                                flooding more extreme.
rond in the lower reaches by linear metres at £400-
                                  Essex rural sea walls have also been ranked by value
£600 m -1 using a sheet piling price of £800-£1000 m -~
                                of land protected per metre length of wall (Wetlands
in conjunction with the cost of building a low bank.
                                Advisory Service, 1992). Urban sectors were excluded
NRA (Anglian Region) have recently costed rond
                                and over 225 km values ranged from £4.25 m -~ to £1
erosion and have concluded that in many locations a
                                m -~ with a mean of £87 m -~. It should be noted that this
cost-effective solution, with added environmental
                                valuation covers area of agricultural land protected by
benefits, is to work to maintain 6 or 7 m of healthy rond
                                sea wall (priced in metre length) as opposed to con-
(NRA (B. Ayling), pets. comm., 1994b).
                                sideration of the price of salt marsh by comparison with
  The saving in sea defence costs allowed by the
                                its functions or products.
presence of salt marsh outweighs the value of agri-
cultural land; this is revealed by a comparison with
                                Salt marshes as part of estuarial and coastal nutrient
current (1993/1994) land prices. Grade 1 agricultural
                                cycles
land is currently sold at between £3950 and £5436
ha -l (£1600 and £2200 acre -1) or 40p-55p m -2. The       Salt marshes are acknowledged to be important sites
                                for the transformation of various materials (Adam,
Agricultural Land Classification grades land from 1
                                1990) but any figures related to primary productivity
(highest quality) to 5 (lowest), the bottom two (4 and 5)
                                tend to be very site specific. Spartina salt marsh in
showing severe limitations to crop production. Essex
                                America has been most frequently studied and Adam
coastal land under cultivation tends to be a heavy grade
                                (1990) has noted that as a result of the spread of S.
3 or 4 and is specific to particular farming methods.
                                anglica the primary production of many salt marshes
Grazing marsh and, salt marsh are both classified as
                                has shown a large increase. In order to consider the
grade 4 land. Agricultural land grades 3 to 4 value from
                                wider economic implications of such a system it is
£2720 to £3000 ha -~ (£1100-£ 1200 acre -1) (27p-30p
                                necessary to view the salt marsh as part of the wider
m -2) for heavy coastal land (up to £3460 ha -1 or £1400
                                estuarine or coastal ecosystem of mudflats, tidal creeks
acre -~ for normal grade 3). Where coastal land is
                                and open water.
unimproved grazing (rare) it is only worth about £740
                                 Comparative studies of four European salt marsh
ha -1 (£300 acre -1) or 7p m -2. According to a national
                                processes are currently being made Lefeuvre et al.
land-owning charity and a leading land management
                                (1993), with the stated aim of determining the relation-
firm, salt marsh will normally sell for £620 to £740
                                ship between salt marshes and adjacent ecosystems,
ha-1 (6-7p m -2, £250-£300 acre-~).
                                estuaries and coastal waters. They report that young,
  In 1994 the Salt Marsh Habitat Scheme (MAFF,
                                building salt marshes are flood-dominated systems and
1994a) was introduced in order to enable payments to
                                net importers of sediments and organic matter while
be made to farmers and landowners over a 20-year
                                exporting mineral nutrient. Mature or over-mature
period for the creation of salt marsh from agricultural
                                marshes (such as those found in Essex), are ebb-
land. Payments are at two levels; £525 ha -~ yr -~ (0.05p
                                dominated and are net exporters of both sediments and
m -2) for land which was arable prior to inundation and
                                organic matter. Boorman & Wells (1993) report a net
£195 ha -~ yr -I (0.02p m -2) for land which was
                                aerial primary productivity from an Essex study site of
permanent grassland. Over the 20 years these payments
                                975 and 1031 dry wt g-i m-2 yr-1 (approximately 10 t
will amount to £10 500 ha -l for former arable land
                                ha -1) for upper and lower marsh, respectively, while
(£1.05 m -z) and £3900 for former grassland (0.39p
                                NRA figures indicate an annual mean of 0.5 t of
m-2). The extent to which these payments are taken up
                                nutrients ha -1 outflowing from the Essex marshes
is likely to relate to a realistic assessment of the balance

                                                           185
                                                 Marine Pollution Bulletin


                               boats, birds and creeks for sale to tourists or art aimed
(NRA, 1992b). This wide difference illustrates the
                               toward a particular sporting theme such as wildfowl
difficulty entailed in the evaluation of primary
                               paintings, the carving of decoy ducks or individual
productivity by different methods and with different
                               yacht portraits in oils.
temporal and seasonal regimes (Carpenter, 1994).
                                 Physical protection is afforded to harbours, marinas
Adam (1990) warns of the danger of extrapolating
                               and sheltered moorings for both working craft and
productivity measurements derived from limited areas
                               yachts. The presence of an entire regional boating
of salt marsh, given its likely wide variations in physico-
                               industry can depend on the proximity of adequate
chemical characteristics.
                               mooring facilities in addition to other historical and
  Salt marshes are widely held to act as nursery areas
                               economic factors and would be virtually impossible to
for some species of fish, which tend to move inshore at
planktonic stage while others visit at high tide on a     price. Some idea of the value of recreational and
seasonal basis. In summer grey mullet browse on algae     working craft moorings can be obtained from the
on the creek banks, bass feed on the invertebrate fauna    situation in the River Blackwater, where an estimated
and flat fish such as flounder and plaice can move into    3000 moorings attract a net profit from rental of well
creeks at high tides. Lobsters find shelter and food     over £1 000 000. Recently a mooring was sold for
beside mooring tackle and eels are commercially fished.    £3000. Many are protected by salt marsh (for example
Essex is the home of a thriving oyster industry and both   Tollesbury Saltings, West Mersea anchorage, Essex)
native oysters (Ostrea edulis) and the hardier, faster-    and although loss of salt marsh would increase the area
growing Pacific oysters (Crassostrea gigas) are produced   available for moorings in a still relatively sheltered
in commercial quantities. The flux of nutrients from the   estuary, much of the character would be lost as would
salt marsh and sheltered farming conditions in the creeks   the sheltered sailing areas. Heavier ground tackle would
are locally attributed to the success of the industry. The  be needed and an increase in damage would be
River Crouch in Essex has a mean summer temperature      expected from strain to boat fittings and from an
several degrees above that of the Solent on England's     increased incidence of failure of mooring gear.
south coast, where first year native oysters are produced   Expensive additional engineering might become
for export to Essex. There is a positive relationship     necessary where marinas are at present protected by
between summer warmth of seawater, influenced by       salt marsh, as is Bradwell marina on the River
heat-absorbing mudflats, and oyster growth (Spencer,     Blackwater by the already-eroding Pewet Island.
1990). Particular value is placed, by oyster farmers, on    The uneasy and artificially promoted partnership of
sites where a concentration of salt marsh nutrients is    farming, recreation and conservation is well illustrated
channelled into a localized area of oyster production and   by the problems involved in the case of salt marsh and
which results in the fattest, most succulent oysters for   sea walls. These sheltered waters provide ideal situ-
sale to the highest quality hotels. The luxury trade from   ations for many recreational watersports (sailing,
Mersea Island on the River Blackwater includes the      swimming, jet-ski riding and water-skiing). Water-skiers
'green-bearded oyster', a speciality which is improved, to  and jet-skiers do considerable erosive damage to the
the gourmet, in taste and colour by a unicellular green    salt marsh edge and in some cases beyond, by using the
alga in the gills. Such oysters are exported to restaurants  edge as a convenient seat and launch pad and by jet-
in Paris, Germany and Belgium, selected in preference to   skiing over the vegetated surface in shallow water at
those produced on the continent by virtue of their      high tide. They can also cause disturbance to nesting,
superior size and flavour.                  roosting and feeding birds. Many stretches of sea wall
  The notoriously fluctuating oyster industry is       include a public footpath along the crest and users of
currently showing an improvement due, it is perceived,    the sea wall, frequently dog-walkers, can cause disturb-
to the decrease of tributyltin (TBT) in local waters     ance to grazing sheep.
(Dowson et al., 1993). No complete figures are available     The suppression of recreational interests would be
for oyster production and sales. It is impossible at     likely to have a beneficial effect on farming and
present to quantify the contribution made by salt marsh    conservation and would also benefit sea defence
nutrients and shelter by values of fish catches and      expenditure. If Essex sea walls were re-profiled with a
shellfish production. Fish and shellfish are not a      longer backslope and were grazed everywhere, the
product of the salt marsh but are an associated un-      public right of way being rescinded, not only would
specified value group, as is the collection of worms for   sheep be protected from dogs and grazing become
personal and commercial bait.                 more feasible, thus encouraging a low cost improve-
                               ment of sea wall quality, but also nesting birds could
Recreation                          return to the sea walls. Pressure from recreation
  Recreational uses can be divided into general and     interests is such, however, that an abandonment of sea
specific user groups, although there are likely to be     wall footpaths is as unlikely as the banning of water-ski
overlaps in some situations. While the latter group      boats and jet-skis from eroding salt marsh areas and the
includes such cases as wildfowling and bird-watching,     need to compromise is accepted by the agencies
the former includes use for watersports and as a scenic    responsible for their care.
backdrop for rambling, dog-walking and sketching. A
                               Salt marsh as wilderness
craft industry has been generated by marshland
atmosphere and ethos as a whole and covers a wide        Apart from pure recreational needs salt marsh is an
range of allied subjects. These include watercolours of    area of open wilderness, possessed of a particular

186
Volume 30/Number 3/March 1995


muted beauty, which is intrinsically valued for its     Ministry of Defence use
existence where it occurs in temperate coastal wetlands.    Owing to their inaccessibility salt marshes are used
This very emptiness has led, until the near present, to it  around the UK by the Ministry of Defence (MOD) as
being treated as wasteland, with little control of      precautionary overshoot buffer zones, which need less
reclamation and development. This situation has now     policing than sea-bound ranges. An example are the
largely changed in Great Britain. While existence value   Fingringhoe ranges in Essex, where the salt marsh is
is essentially non-use, as it refers to willingness to pay  managed for wildlife by the Essex Wildlife Trust and
for the existence or preservation of natural resources, it  benefits from the lack of disturbance generated by the
may be of great magnitude. In Essex salt marshes are     range. Inland ranges have buffer zones of moorland or
seldom used, apart from the dry footpath along the      farmland, the latter rented for minimal return since
adjacent sea wall, as a place to walk because they are so  access is affected. Ranges which fire out to sea have
difficult to traverse. In areas where the vegetation is   attendant craft to police the water. A depressed rent is
firmer, the substrate less muddy and the levels higher,   paid for MOD farmland as a result of restrictions in
as in the north Norfolk coast, the salt marsh is utilized  use. There is a lack of available information on rents
for walking and swimming to a far greater extent,      and on the cost of policing marine ranges and co-
engendering an option value for those able to visit the   operation would be required from the MOD for
locality, both the resident population and tourists from   valuation purposes.
further afield. In the more remote areas access
problems, with the only footpaths provided by wild-
                               Discussion
fowlers for their own purposes, protect the salt marsh
from overuse in most situations. A portion of the salt     It has been established that land for wildfowling
                               purposes has the highest direct value, however the
marsh flora is susceptible to damage by trampling
                               highest single value of salt marsh is the enormous
(Adam, 1990), the soft substrate facilitating the
shearing and compacting forces which damage soil       saving it can afford to capital sea defence costs (see
                               Table 2). Ironically, the narrower the strip of salt marsh
structure while vulnerable vegetation suffers physical
                               outside a sea wall, the greater the potential saving on
damage. A combination of these effects can cause
                               building or maintenance costs, a reflection of the vastly
localized changes to occur.
                               escalated structural costs of sea walls in unprotected
                               situations, and the greater the value of the salt marsh.
Education and scientific research              The value of salt marsh to sea defences in many parts of
                               the UK are now in need of extensive repair or replace-
  Salt marsh provides rich grounds for research on
                               ment (Farndale, 1993), thus facing a rapid escalation in
plants and animals which might have a beating on
                               costs, a situation that has been compounded by the
future economics (such as toleration of salinity and
plant mechanisms for resistance to stress) and they are   continuing loss of salt marsh. It has been calculated that
                               complete loss of all Essex salt marsh would incur
also valuable teaching resources, allowing access to
                               minimum costs of over £600 million for rebuilding of
studies on plant zonation and resistance of flora and
                               sea walls. Salt marsh should consequently be regarded
fauna to a medley of environmental parameters.
                               as a valuable asset.
                                The disparity between the generally low price of salt
                               marsh as a land commodity as opposed to its high value
Value of salt marsh to conservation
                               in sea defence terms reflects the lack of a high value
  High numbers of waders and wildfowl, many making
                               direct product unless a quality wildfowling site is
seasonal use of the rich invertebrate fauna and
                               involved. Owners of salt marsh are frequently not the
associated plant life, feed on the mudflats at the outer
                               beneficiaries of its buffering effect. It can be the sea
boundaries of the vegetated area and use the salt marsh
                               defence authorities, funded by the tax payer, or the
and grazing marshes as shelter, roosting grounds and in
                               owners of land inside the sea wall who stand to gain.
some cases feeding grounds at high tide. At the time of
                               Direct values derived from salt marsh can be summed
the proposal in the 1970s for the third London airport
                               with sea defence value, although care should be taken to
to be built on Maplin sands, extensive ecological studies
took place (Boorman & Ranwell, 1977) following
which extensive areas of the Essex coast were given                    TABLE 2
statutory protection (as Sites of Special Scientific              Comparison of uses and values.
Interest (SSSI) and National Nature Reserves (NNRs)),
                               Uses and values                   Value £ m -z
in order to protect what was seen as a threatened and
extremely valuable habitat. Eighty percent of the salt    Sea defence: capital savings              30-60
                                     maintenance savings            0.6
marsh in the British Isles is currently scheduled as SSSI
                               Wildfowling (sales)                  0.4-1
(Davidson, 1991). The area now includes sites               (annual licence)              0-0.5
protected under the RAMSAR convention (for the        Grazing                         0.15
                               Grade 1 agricultural land              0.44-0.6
protection of bird habitat) and was declared an
                               Grade 3 agricultural land                0.35
Environmentally Sensitive Area (ESA) by MAFF in       Essex coastal land, Grade 3               0.3
March 1994 (MAFF, 1994b). This will attract         Salt marsh                       0.6
                               Unimproved grazing marsh                0.6
additional grant aid to coastal farmers for environ-
                               M A F F Habitats scheme (yr -1)           0.02-0.05
mental enhancement.

                                                                187
                                                 Marine Pollution Bulletin


                               coastal defence is not only just one of the issues
ensure that these activities are mutually compatible
                               covered by such procedures but is also that which is
before multiple uses are implied by their addition.
                               most easily subject to authoritarian claims for un-
Indirect uses beyond those of sea defence (such as those
                               sypathetic engineering requirements. An integrated
derived from specific recreational activities or the less
                               approach to wetland management, guided by an
tangible functions or values), can be expected to evince
                               enabling authority not subject to ministerial and depart-
further positive values.
                               mental power struggles, might result in combined
  Pethick (1993) has indicated that attempts to retain
                               management of riverine flood defence with agricultural
the status quo in an estuary by protecting salt marsh
                               set-aside (the decommissioning of agricultural land to
from erosion are likely to exacerbate the instability of
                               reduce surplus production) which is currently under fire
the system as natural processes rework the sediment
                               for its lack of environmental benefit. By targeting river
toward a wider and shallower profile. Salt marsh is at
                               flood plains buffer zones of washland could be
present protecting much of the Essex sea wall frontage
and several experimental schemes are underway to       provided with the added benefit of creation of wetland
                               habitat. Similar principles applied to coastal issues by
investigate means of stimulating salt marsh develop-
                               the same potential authority would readily embrace
ment and reducing erosion. A scenario of continuing
salt marsh loss and the building of ever more massive    such themes as managed retreat and the integrated
                               management of complete estuarial systems.
sea walls is aesthetically displeasing and financially
inappropriate, although without funding constraints the     Although coastal defence authorities have taken note
Dutch solution of a concrete coastline might become     of the coastal defence implications, others who may be
more politically pleasing. It is even possible to envisage  adversely affected by salt marsh loss are as yet un-
habitat creation in such circumstances, incorporating    concerned. Yacht servicing agencies might well start to
design of sea defences as artificial cliffs and hard     count the cost of loss of protection for their estuarine
intertidal surfaces which are uncommon in East Anglia.    moorings, should the present rate of salt marsh-loss
A different long-term approach to sea defence is       continue. The servicing of sporting and leisure activities
required and managed retreat has recently become a      linked with salt marsh is of great significance. For
contender in sea defence options. The term 'managed     example, the yachting industry (marinas, boatyards,
retreat' has been defined as 'the concept of retreating   sailmakers, chandlers, clothing, victualling, club
inland from the existing line of flood defence or coast   administration, public houses and the yachting press)
protection works, while monitoring and maintaining an    and the wildfowling industry (guns, ammunition,
awareness of the consequences of the retreaf (Birks,     clothing, dogs for breeding and training and the
1993). Where land to be inundated in the course of      shooting press). A future scenario of complete salt
retreat is of a sufficient height above sea level the    marsh loss over wide areas may indicate a complete
operation can be managed with an intention to create     change in patters of coastal leisure activity. Proprietary
salt marsh as protection for low, inexpensive sea walls   interests in shoreside facilities or moorings threatened
or as the sole protection where a gradual rise in the land  with degradation and exposure are of more immediate
occurs. This is now regarded by MAFF as an option to     concern, since strong local lobbies can drive attempts to
be considered in benefit-cost appraisal of coastal      maintain local protection to the detriment of the wider
engineering schemes and is thus an integral part of     environment. Local concerns should be fully informed
valuation of salt marsh as a sea defence (MAFF,       of the developments in understanding of this emotive
1993b). However, Pethick (1993) warns that retreat      situation.
projects implemented with insufficient awareness of the     While recreation interests are frequently vociferously
implications to estuarine tidal regimes may increase     championed, a further blow to local economies in many
degradation and erosion by causing an increase in tidal   parts of the world will be the effect on already
prism and water velocities. In the delicate situation of   beleaguered coastal fisheries. If a proven link could be
salt marsh loss which is currently the subject of      made between fisheries, in particular the oyster fishery
considerable research, no single solution is likely to be  in the case of Essex, a direct value could be assigned to
found. A multi-disciplinary approach is being taken in    salt marsh from the profits of that industry. Oyster
order to reach a workable strategy for the future.      production and other inshore fisheries which currently
  With the development of greater understanding of     benefit from salt marshes, however indirectly, could feel
sediment sources and transport and concern about       measurable adverse affects if widespread salt marsh loss
engineered coastal structures, has come a view held by    continues. That some linkage with the oyster industry
an increasing number of engineers and scientists that    occurs is indisputable but that the oyster fisheries
the coastline should be treated in its entirety. A      depend on salt marsh for their existence is not. In the
piecemeal approach to coastal defence, combined with     UK, many values are less clear-cut than those from the
lax control on activities such as dredging, is blamed for  USA since fisheries are not seen to depend on salt
exacerbating problems of coastal land loss by erosion    marsh in the same way. Small amounts such as rental of
while also starving low-lying accreting coastlines of    oyster pits for peppercorn rents still change hands but
material with which to maintain a balanced sediment     since these sums are invariably below three figures and
budget. A current tendency towards coastal zone       are mostly kept up as an insurance against future need
management within coastal cells only partially        as opposed to current use, they can hardly be con-
addresses the issue, since it is unlikely that sediment   sidered in the same scale of calculations. With no
movement is restricted entirely to closed cells and     proven linkage, oyster production should not be

188
Volume 30/Number 3/March 1995

included in direct valuation but could be considered as           Dowson, P. H., Bubb, J. M. & Lester, J. N. (1993). Temporal distribu-
                                        tion of organotins in the aquatic environment. Mar. Pollut. Bull. 26,
a value awaiting further studies on estuarine food webs            487-494.
and in particular work on the effect of a concentration           Farndale, N. (1993). How cruel the sea. Country Life, 25 March, 64-
of salt marsh nutrients on speed of growth and eventual            67.
                                      Gibson, J. (1993). Managed retreat: incentives and legal issues.
size of oysters. Placement of fisheries under 'indirect            Proceedings of seminar on managed retreat, 17 March 1993,
value, value unknown' may be more acceptable at                London Zoo, London, UK.
present.                                  Gosselink, J. G., Odum, E. E & Pope, R. M. (1974). The value of tidal
                                        marshes. Center for wetland resources, Louisiana State University,
  Valuation of salt marsh as a sea defence can be               Louisiana, USA.
deemed a separate exercise from the complete valuation           Grieve, H. (1959). The Great Tide. County Council of Essex,
                                        Chelmsford, UK.
of salt marsh as an abstract, multi-faceted ecosystem
                                      Hufschmidt, M. M., James, D. E., Meister, A. D., Bower, B. T. & Dixon,
and this has yet to be satisfactorily achieved. Changing            J. A. (1983). Environment, Natural Systems and Development. An
perspectives on salt marsh, which was once regarded as             Economic Valuation Guide, p. 197. John Hopkins University Press,
                                        London.
intertidal wasteland open to improvement and develop-
                                      Hydraulics Research (1987). Saltings as a sea defence. Report to NRA
ment, have led toward higher valuation in a sphere               Anglian Region. 35 pp.
which is somewhat removed from the field of con-              Institute of Estuarine and Coastal Studies (1993). Essex Saltings
                                        Research. Report to NRA Angiian Region. 54 pp.
servation and wildfowling organizations. It was not,
                                      Intergovernmental Panel on Climate Change (undated). Climate
however, until the loss of this important habitat               Change The 1PCC Response Strategies. World Meteorological
impinged upon the economic viability of sea defences              Programme/United Nations Environment Programme, pp. 129-159.
                                      Lefeuvre, J. C., Dunkers, N., Boorman, L., Loveland, P. & Bettencourt,
that projects were commissioned to stem erosion and
                                        A. (1993). Comparative study on salt marsh processes, EEC
create new salt marshes. With continued salt marsh               Contract No. Ev4v-0172-F, University of Rennes, France.
decline and forecast sea level rise, increased emphasis           Long, S. P. & Mason, C. E (1983). Saltmarsh Ecology. Blackie,
                                        Glasgow, UK.
will be placed on its value in both economic and
                                      MAFF (1993a) Coastal defence and the environment. MAFE London,
aesthetic terms and in areas of extensive coastal               UK.
wetlands, a subtle reshaping of coastal topography will           MAFF (1993b). Strategy for flood and coastal defence in England and
                                        Wales. MAFF, London, UK.
occur. The eventual contribution of salt marsh in terms
                                      MAFF (1994a). The salt marsh habitat scheme: guidelines for farmers.
of sea defence, recreation, fisheries and its less tangible          MAFF, London, UK.
functions will be a product of the research-led policy           MAFF (1994b). The Essex coast ESA: guidelines for farmers. MAFE
                                        London, UK.
decisions which are made in the near future.
                                      National Rivers Authority (1991a). Shoreline management--the
                                        Anglian perspective. Proceedings of conference, The future of
                                        shoreline management. 14 October 1991. National Rivers Authority,
                                        Angiian Region.
One of the authors (S.K.) is grateful to SERC and ESRC for the
                                      National Rivers Authority (1991b). Essex Local Flood Defence
provision of studentship. Thanks are due to the NRA (Anglian Region)
                                        Committee Annual Report 1990/1991. National Rivers Authority,
for their co-operation in the preparation of this manuscript.
                                        Anglian Region.
                                      National Rivers Authority (1991c). Norfolk and Suffolk Local Flood
                                        Defence Committee Annual Report 1990/1991. National Rivers
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Adam, E (1990). Saltmarsh Ecology. Cambridge University Press,
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Barbier, E. B. (1989). The Economic Value of Ecosystems: 1--Tropical
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Barbier, E. B. (1993). Sustainable use of wetlands, valuing tropical
                                      National Rivers Authority (1992c). Norfolk and Suffolk Local Flood
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  Geograph. Z 159, 22-32.
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Birks, C. J. (1993). Managed retreat: putting the theory into practice,
                                      National Rivers Authority (1993a). Essex Local Flood Defence
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Boorman, L. A. (1992). Studies of salt marsh erosion in Essex. Project
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